This invention relates to a multiwell test apparatus suitable for promoting fluid interactions such as by monitoring cell metabolism within wells of the test apparatus. More particularly, this invention relates to such a multiwell test apparatus comprising a multiwell filter plate and a receiver plate which permits adding or removing liquid from the receiver plate without disturbing a material such as cells within the wells of the multiwell filter plate.
At the present time, multiwell test apparatus for testing samples include a multiwell filter plate, a feeding tray, a multiwell receiver plate and a lid. The wells of the multiwell filter plate are formed of a hollow, typically tubular, member with an open end to which is attached a membrane such as a microporous membrane. The tubular members can be inserted into a feeding tray containing a nutrient medium so that cells in the wells can be attached to the membrane and grown thereon. The cells are fed as nutrients pass from the nutrient medium through the membrane and to the cells at a rate controlled by the concentration gradient of nutrients from the medium to the cells. The nutrient medium in the feed tray is periodically replenished to maintain cell growth.
After the desired level of cell growth on the membranes of the wells has been attained, the multiwell filter plate can be utilized in conventional assay methods. These assay methods generally are effected by positioning the membranes and cells on the multiwell filter plate into the wells of the multiwell receiver plate, such as a 96 well receiver plate positioned below the multiwell filter plate or it just has to have the same number of wells in register with the cell/filter plate. The wells of the multiwell receiver plate contain a liquid composition to be assayed. The composition to be assayed diffuses into and then through the membrane. The resultant liquid products within the wells of the multiwell filter plate or in the wells of the multiwell receiver plate then are assayed to determine the capability of the composition being assayed to permeate the cell barrier.
An important component in the drug discovery and development process is the determination of the oral absorption and bioavailability of new compounds. In order to perform this evaluation in a cost effective, high throughput and sensitive assay, it is ideal to use an in vitro device with a multitude of wells containing cells, a small amount of assay material and automation. Classically, the determination of in vitro oral absorption characteristics is performed using a defined epithelium cell line and measuring the apparent transport rate of the drug across a monolayer of the cells. More recently it is possible to rank/order the passive transport rate of potential drug candidates using an artificial membrane barrier. The values generated from these in vitro experiments are valuable methods for screening the most likely successful drug candidates long before the oral absorption rate are validated by in vivo measurements. A typical experiment for determining the drug absorption characteristics of a known or unknown chemical compound is performed as follows. The multiwell device is seeded with epithelium cells on top of the filter in a defined nutrients medium. The same medium is also added to the single well feeding tray located below and in fluid contact with the device containing the cells. The cells are allowed to proliferate and differentiate over a number of days. The nutrient medium is periodically replaced with fresh medium to replenish exhausted nutrients and remove waste and dead cells. At the end of a growing time, the cells and multiwell device are gently washed with an isotonic buffer to remove protein and residual nutrient medium. At this time, the multiwell filter plate is transferred to the multiwell receiver plate and the chemicals to be assayed are introduced to either the compartment above the cell layer or below the cells and filter support in the multiwell receiver tray. The opposing chamber is filled with drug free buffer and the multiwell device is incubated for some period of time, typically at 37 degrees Centigrade with shaking. If multiple time points are desired, sampling from either compartment can be achieved without separating the device. The amount of drug/chemical that is transported across the cell barrier can be determined by a variety of analytical methods, but typically is determined using LC-MS/MS (Liquid Chromatography-Mass Spectrometry-Mass Spectrometry).
In prior art design, cross-talk between wells occur between the multiwell filter plate and a multiwell receiver plate due to capillary forces between the outside walls of the filter plate wells and the inside walls of the receiver plate wells. These forces result in liquid in the multiwell receiver plate moving up the wall of the well to the top of the multiwell receiver plate resulting in spill-over into an adjacent well and contamination. This contamination is unacceptable.
In addition, the multiwell filter plate and the receiver plate, be it a single well feeding tray or a multiwell receiver plate must be easily separated from each other, particularly when the multiwell test plate is processed in an automated environment.
It is also desirable to remove any droplets of liquid retained on the lower surfaces of the membranes during removal of the multiwell filter plate from the liquid in the wells of the receiver plate albeit a single well feeding tray or a multiwell receiving plate.
Accordingly, it would be desirable to provide a multiwell test apparatus comprising a receiver plate and a multiwell filter plate which facilitates removal of excess liquid from the wells of the multiwell filter plate. In addition, it would be desirable to provide such a multiwell test apparatus which prevents liquid transfer from well to well when the multiwell filter plate and the multiwell receiver plate are positioned together.